Incorrect Use of Glass Only Values for Glazing Energy Performance Ratings

10 October 2014

The AWA has been made aware that last week three South Australian window companies advised energy raters to use Glass only U-values (UGLASS, UCOG, UG) and SHGC (SHGCGLASS, SHGCCOG, SHGCG) in the absence of immediately available window (glazing) results to carry out building performance ratings.

This advice contravenes the Australian Standard for Windows and Glazed Doors - AS 2047, the National Construction Code (NCC) and the Australian Consumer Law Act. There is a growing number of dispute resolution and court actions against architects, energy raters and window companies on the east coast and this will increase if incorrect results or products are supplied at a time when home and building owners are challenging the performance outcomes of their selections.

This is not a single state or territory issue, it is national. The AWA we would like to advise all members and the industry in general that ONLY whole window system U-value’s (UWINDOW, UW) and SHGC’s (SHGCWINDOW, SHGCW) can be used. Under the NCC, within Building Code of Australia (BCA), energy efficiency provisions for Volume One, Section J2.4 Glazing and Volume Two, Section 3.12.2.1 External Glazing state that external glazing performance data must be determined in accordance with the guidelines of the Australian Fenestration Rating Council (AFRC).

The BCA States:

In Volume 1
J 2.4 (a) “The glazing in each storey, including any mezzanine, of a building must be assessed”

And in Volume 2
3.12.2.1 (a) “The aggregate conductance of the glazing in each storey”
3.12.2.1 (b) “The aggregate solar heat gain of the glazing in each storey”

The BCA goes further with Volume 1, A 1.1 and Volume 2, 1.1.1 defining Glazing as

“a transparent or translucent element and its supporting frame located in the envelope, and includes a window other than a roof light.”

The BCA also provides the following explanatory information in the Guides for Use:

“By referring to ' glazing elements', 3.12.2.1” and J2.4 “require Total System U-Values and Total System SHGCs to be assessed for the combined effect of glass and frames. The measurement of these Total System U-Values and Total System SHGCs is specified in the Technical Protocols and Procedures Manual for Energy Rating of Fenestration Products by the Australian Fenestration Rating Council (AFRC).”

Energy ratings through AFRC accredited energy raters are the only acceptable performance results for use with the BCA Glazing Calculators (Volume 1 and 2), BASIX and NatHERS Software tools (AccuRate and FirstRate)

AS 2047 states:

2.3.3 Window energy rating

Calculation of the total system overall heat transfer coefficient (U-value), the total system solar heat gain coefficient (SHGC) and the visible transmittance (Tvis) shall be required for the total system of the window assembly.

The Australian Consumer Law states:

A major failure in supply of goods or services occurs when goods are significantly different from their description or demonstration model, the goods or services are unfit for their purpose and cannot easily be remedied in a reasonable time, goods or services are unfit for the purpose made known to the supplier and cannot be remedied within a reasonable time. Using glass only values contravenes all of these obligations.

Not using total window (glazing) system values to Australian approved procedures and environmental conditions can result in significant under or over performance of the building envelope, especially in buildings with large glazed areas. The stated performance of the building will not meet the energy efficiency provisions of the BCA.

If members require assistance or training on how to select or validate compliant products for simulation or using BCA glazing calculators, this is freely available to you as part of your membership. Please contact WERS directly in the Sydney office for further advice.


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